Techniques for the production of a hard copy from soft information are being used as a result of the recent progress which has been made with information processing and storage and with techniques for image processing, and as a result of the use of communication circuits. In addition, very high quality photographic prints can easily and inexpensively be provided as a result of the progress which has been made with silver halide photosensitive materials and compact, rapid and simple development systems (for example, the mini-lab system). Therefore, there is a great demand for that inexpensive hard copies with the high picture quality of photographic prints can be obtained easily from soft information.
Conventional techniques for the provision of a hard copy from soft information have included those, in which photosensitive recording materials are not used, such as the systems in which electrical signals and electromagnetic signals are used and ink jet systems. Other conventional techniques in which photosensitive materials are used include silver halide photosensitive materials and electrophotographic materials. In the latter case, there are systems in which recordings are made with an optical system which emits controlled light in accordance with the image information, and this enables not only optical system production, image resolution and binary recording but also multi-tone recording to be achieved. These systems are useful for obtaining high image quality. The use of silver halide photosensitive materials are more convenient than systems in which electrophotographic materials are used since image formation is achieved chemically. However, systems in which silver halide photosensitive materials are used must have photosensitive wavelengths which match the optical system, the stable sensitivity, latent image stability, resolution, color separation of the three primary colors, and rapid and simple color development processing with attention given to cost.
In the past, copying machines wherein electrophotographic techniques are used, laser printers, silver halide based heat developable dye diffusion systems, and Pictrography (a trade name: made by the Fuji Photographic Film Co.) which used LED's existed as a color copying technique.
Color photographic materials which use at least three silver halide emulsion layers with the usual color couplers are formed on a base. These layers are not exposed using visible light but at least two of the layers are sensitized to laser light in the infrared region. The fundamental conditions for these materials are disclosed in JP-A-61-137149. (The term "JP-A" as used herein signifies an "unexamined published Japanese patent application".)
In JP-A-63-197947, full color recording materials in which a unit of at least three photosensitive layers which contain color couplers is provided on a support are disclosed. At least one layer is formed in such a way that it is photosensitive to LED or semiconductor laser light, being spectrally sensitized in such a way that the spectrally sensitized peak wavelength is longer than about 670 nm, and with which color images can be obtained by means of a light scanning exposure and a subsequent color development process. More precisely, a method of spectral sensitization which is stable and provides high speed, and a method of using dyes are disclosed in JP-A-63-197947.
In the specification of JP-A-55-13505, a color image recording system using a color photographic material in which yellow, magenta and cyan color formation is controlled with three light beams which have different wavelengths, for example, green, red and infrared light beams, respectively, is disclosed.
The basic conditions for a continuous tone scanning type printer semiconductor laser output controlling mechanism are described by S. H. Baek on pages 245-247 of the published papers of the Fourth International Symposium (SPSE) on Non-impact Printing (Mar. 23, 1988).
Devices in which light-insensitive recording materials are used for obtaining a hard copy from soft information are effective for low image quality results, but it is virtually impossible to obtain photographic print type picture quality with A4 to B4 or smaller sizes which are normally used. Even though the cost per sheet is low, the cost is high when picture quality (for example, recording content:density.times.surface area) is taken into account. The image quality with electrophotographic systems is worse than that obtained with silver halide photosensitive material systems. Also the image forming process is more complex mechanically and it is difficult to obtain a hard copy in a stable manner.
On the other hand, high image quality is readily obtained with systems in which silver halide photosensitive materials are used, but the photosensitive materials themselves must be provided with photosensitive wavelengths which match the optical system, stable sensitivity, latent image stability, and separation of the three primary colors etc. The semiconductor lasers which are used in the present invention have a generating device which can be obtained inexpensively and which is more compact than that required with gas lasers. But, contrary to expectation, the emitted light intensity and the emission wavelength regions are unstable, and with a semiconductor laser light of comparatively short wavelengths, the modulation tolerance band of the current dependence of the emission intensity is narrow in practice and special steps must be taken in the silver halide photosensitive material to reproduce the excellent image quality of the silver halide photosensitive materials. First, the spectrally sensitized wavelength region of each photosensitive layer must be sufficiently wide (for example, 40 to 60 nm wide), and there must be little overlap of the sensitive wavelengths of the various photosensitive layers. For example, the difference in photographic speed from the other layers at the principal sensitive wavelength of a photosensitive layer should be at least 0.80 (logarithmic representation). Second, the latent image obtained with an exposure time of 10.sup.-6 to 10.sup.-8 second must be stable, and the gradation represented by a photographic characteristic curve must be sufficiently linear in the exposure region (represented by logalithm) above 1.0, and preferably in the exposure region above 1.5.
No mention is made of these important points in the afore-mentioned JP-A-55-13505 or in the aforementioned paper by Baek et al. The basic structure of the color photosensitive materials is disclosed in the afore-mentioned JP-A-61-137149 (corresponding to EP 183528), but there is no actual disclosure of the preferred means of achieving this structure. Practical performance cannot be obtained with the color photosensitive materials indicated in Examples 1 to 10. Moreover, there is no disclosure of a practical means of using these silver halide photosensitive materials.
Silver iodobromide emulsions, silver bromide emulsions and silver chlorobromide emulsions are known as silver halide emulsions used in silver halide photosensitive emulsions which can be exposed using laser light beams. The color development processing of full color recording materials should be rapid, taking not more than 60 seconds, to match the rapidity of the exposures which are made with an output device with semiconductor laser light beams used in the present invention. Silver halide emulsions which have a high silver chloride content are useful for this purpose. However, it is difficult to provide infrared sensitivity to wavelengths above 670 nm, and especially to wavelengths above 750 nm, with silver chlorobromide emulsions which have a high silver chloride content, especially when the silver chloride content is above 95 mol %. There are three reasons. First, the high speed is affected, and the production and storage stabilities are poor. It is especially difficult to obtain good linear gradation at high photographic speed and difficult to obtain a sharp spectral sensitivity distribution. Second, it is difficult to obtain high photographic speeds with short exposure times, for
example, of from 10.sup.-6 to 10.sup.-8 seconds. Finally, the adsorpability of a sensitizing agent on the silver halide grains is low. If color couplers and high concentrations of surfactants or organic solvents are present, a decrease of photographic speed and fogging are liable to occur during dissolution of the emulsion and ageing. Hence, the discovery of a technique which provides high photographic speed even when silver halide emulsions which have a high silver chloride content are used, and which provides excellent latent image stability with rapid processing is desirable.